Respiratory or breathing assistance devices or systems for providing a flow of humidified and heated gases to a patient for therapeutic purposes are well known in the art. Systems for providing therapy of this type (for example respiratory humidification) typically have a structure where gases are delivered to a humidifier chamber from a gases source, such as a blower (also known as a compressor, an assisted breathing unit, a fan unit, a flow generator or a pressure generator). As the gases pass over the hot water, or through the heated and humidified air in the humidifier chamber, they become saturated with water vapour. The heated and humidified gases are then delivered to a user or patient downstream from the humidifier chamber, via a patient interface comprising a flexible gases conduit and a patient interface.
In one form, such respiratory assistance systems can be modular systems that comprise a humidifier unit and a blower unit that are separate (modular) items. The modules are connected in series via connection conduits to allow gases to pass from the blower unit to the humidifier unit. For example, FIG. 1 shows a schematic view of a user 1 receiving a stream of heated and humidified air from a modular respiratory assistance system. Pressurised air is provided from an assisted breathing unit or blower unit 2a via a connector conduit 7 to a humidifier chamber 4a. The stream of humidified, heated and pressurised air exits the humidification chamber 4a via a flexible hose or gases conduit 3, and is provided to the patient or user 1 via a patient interface 5.
In an alternative form, the respiratory assistance systems can be integrated systems in which the blower unit and the humidifier unit are contained within the same housing. A typical integrated system consists of a main blower unit or assisted breathing unit which provides a pressurised gases flow, and a humidifier unit that mates with or is otherwise rigidly connected to the blower unit. FIG. 2 shows a schematic view of the user 1 receiving heated and humidified air from an integrated respiratory assistance system 6. The system operates in the same manner as the modular system shown in FIG. 1, except the humidification chamber 4b has been integrated with the blower unit to form the integrated system 6.
The patient interface 5 shown in FIGS. 1 and 2 is a nasal mask, covering the nose of the user 1. However, it should be noted that in systems of these types, a mask that covers the mouth and nose, a full face mask, a nasal cannula, or any other suitable patient interface could be substituted for the nasal mask shown. A mouth-only interface or oral mask could also be used. Also, the patient or user end of the conduit can be connected to a tracheostomy fitting, or an endotracheal intubation.
Impeller type fans or blowers are most commonly used in respiratory assistance systems of this type. An impeller blade unit is contained within an impeller housing. The impeller blade unit is connected to a drive of some form by a central spindle. A typical impeller housing is shown in FIGS. 3 and 4. A typical rotating impeller unit 10, having a plurality of blades 11 and a shroud 12, which in use is located inside the housing is shown in FIGS. 5 and 6. Air is drawn into the centre of the impeller unit through an aperture, and is then forced outwards from the centre of the housing towards an exit passage (usually located to one side of the housing) by the blades of the rotating impeller unit. The blades 11 are coupled to the central spindle 13, which is rotated by a motor for example.
The respiratory assistance systems of the type described above typically present various problems or challenges to the manufacturer from a design viewpoint, some of which are briefly outlined below.
Effective respiratory therapy often requires a user to use respiratory assistance systems of the type described above on a daily basis for long periods of time. For the treatment of OSA, the user needs to use the respiratory assistance system at night when they are asleep. Patient comfort and convenience when using such respiratory assistance systems is paramount to compliant and effective treatment. Mask leaks are a common complaint of user's of the above type of respiratory assistance systems. Mask leaks are typically caused by the flexible gases conduit 3 tugging on the patient interface or mask 5 when the user moves in their sleep.
Most respiratory assistance systems of the type described above for treating OSA with PAP therapy provide a gas supply to the patient interface but have no return path for gases from the interface. To eliminate the build-up of carbon dioxide in the patient interface, the patient interface requires a gas washout vent for venting exhaled gases to atmosphere, and this is often referred to as the ‘bias flow’. The bias flow represents a loss in the gases supply circuit and the blower unit must have a motor that is powerful enough to maintain the bias flow while also generating the desired gas pressure at the patient interface. The gas washout vent can also become a source of noise and a source of discernable draughts. Excessive noise can be irritating for the patient and their bed partner. Depending on their location, draughts can also be annoying to the patient.
Humidification of the gases in the respiratory assistance systems also adds to the design complexity. For example, heating of the gases conduit 3 of the patient interface is often required to prevent condensation forming in the gases conduit.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.
It is an object of the present invention to provide an improved respiratory assistance apparatus, or to at least provide the public with a useful choice.